BiMOS devices that include a bipolar transistor and a metal-oxide-semiconductor field-effect transistor (MOS transistor) as a trigger for the bipolar transistor have been used for years. In many of these devices, the bipolar transistor, which is part of a pnpn thyristor, and the MOS transistor share the same regions, or the source and drain of the triggering MOS transistor are connected to the p-type regions or the n-type regions of the thyristor. In the former, the collector and drain are part of the same region, the base and channel region are part of the same region, and the emitter and source are part of the same region. In this case, both the bipolar and MOS transistors cannot be optimized. Optimizing characteristics of the bipolar transistor typically affects the characteristics of the MOS transistor. In order to improve the characteristics of both transistors, the base and channel region may be separated. In the latter, the collector and drain are electrically connected together, and the emitter and source are electrically connected together, but the base and channel regions are separate. Because the base and channel regions are separate, many of the characteristics of the bipolar transistor may be adjusted separately from the characteristics of the MOS transistor. Still, the uses of the BiMOS device may be limited because the collector and drain are electrically connected and the emitter and source are electrically connected together. A high potential on the collector will also be on the drain and may cause channel punchthrough within the MOS transistor.
Many of the BiMOS devices described above have a bipolar transistor that is triggered by the MOS transistor. The base or channel regions in these types of devices are typically connected to something else. To be more specific, the base or channel region is typically connected to about ground potential, V.sub.DD or another component. In any event, the base or channel regions are not allowed to electrically float.